<!DOCTYPE html>
<html lang="zh">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>弹性伸缩比</title>
  <style>
    .header {
      display: flex;
      margin: 0 auto;
      width: 1200px;
      height: 44px;
    }

    .header .user {
      flex: 1;
      background-color: #f00;
    }

    .header .search {
      flex: 2;
      background-color: #0f0;
    }

    .header .icon {
      flex: 1;
      background-color: #00f;
    }
  </style>
</head>

<body>
  <div class="header">
    <div class="user">1</div>
    <div class="search">2</div>
    <div class="icon">3</div>
  </div>
</body>

</html>